1. Field of the Invention
The present invention relates to a partial discharge measurement method, a partial discharge measurement device, and a method of producing an insulated wire.
2. Description of the Related Art
An insulated wire includes an insulating layer so as to cover an outer periphery of a conductor. In the insulated wire, the application of a high voltage to the conductor generates an electric field around the insulating layer, and an increase in the electric field strength causes a partial discharge event from the insulating layer. The occurrence of the partial discharge event causes the insulating layer to deteriorate, and may finally result in a dielectric breakdown.
Thus, in order to prevent a dielectric breakdown due to a partial discharge event when an insulated wire is used in an electrical device or the like, it is necessary to ascertain in advance what level of an applied voltage causes a partial discharge event, that is, the level of a voltage at which a partial discharge event begins to occur, which is called “partial discharge inception voltage” (hereinafter also referred to as PDIV). In particular, in recent years, in an electrical device, such as a motor, inverter control has been performed from the viewpoint of high efficiency, the occurrence of a surge voltage has resulted in the application of a high voltage to an insulated wire constituting the motor or the like, and thus it has become increasingly important to ascertain a PDIV of an insulating layer.
An example of a method of measuring a PDIV is a method in which part of a produced insulated wire is extracted as a sample, a voltage is applied between the terminals thereof, and the occurrence or nonoccurrence of a partial discharge event due to the application of voltage is measured by using an optical sensor (generally, a photomultiplier, an electromagnetic-wave sensor, or the like), a quantity of charge discharged, a current value, and so forth (see, for example, Japanese Unexamined Patent Application Publication No. 2008-82904).